When water is to be pumped out of an outdoor pit, reservoir, or canal, it is important to prevent debris, such as leaves, sticks, discarded plastic and paper articles, stones, etc., from entering the pump. Rotary self-cleaning strainers that contain cylindrical screens for performing the straining function are often used for this purpose.
The strainer is attached to the end of a conduit and immersed in the body of water that is to be pumped. The pump is operated to suck water through the strainer and conduit, as the strainer screen prevents debris from being sucked into the conduit along with the water. Certain debris may adhere to the screen's exterior due to the pump suction force. However, the continued adherence of such debris to the screen's exterior, and resulting impairment of flow through the screen, is prevented by rotating the screen past a nozzle structure which is disposed on the interior of the screen and directs water outwardly through the screen to dislodge the debris. The water is fed under pressure to the strainer through a separate supply line which may be tapped into the pump's outlet. The water acts on only a limited circumferential zone of the screen at any given time to force adhering debris away from the exterior of the screen as the screen revolves past the nozzle structure. The remainder of the screen serves to conduct the flow of liquid that is being pumped out of the pit or reservoir through the screen and into the conduit.
The inventors, commonly assigned U.S. Pat. No. 4,822,486 issued Apr. 18, 1989, discloses a new and improved rotary self-cleaning strainer of this general type. The patented strainer possesses a number of novel and unique features which individually and collectively constitute the improvements. One feature relates to the manner in which the nozzle structure that performs the self-cleaning function is organized and arranged in assembly with other component parts to impart rotation to the screen.
Some aspects of the present invention relate to improvements which are specific to the invention of U.S. Pat. No. 4,822,486; other aspects to improvements which are applicable to rotary self-cleaning strainers that do not necessarily embody the invention of U.S. Pat. No. 4,822,486.
The present invention arises in consequence of the recognition that certain existing irrigation systems which could benefit from the use of the patented strainer lack pumps of sufficient delivery pressure for securing the most effective usage of the patented strainer, and that for any of a number of different reasons, adaptation of these systems to provide higher pressures for operating the patented strainer in systems is often improbable. For example, a typical crop irrigation system falling into this category may comprise an extensive network of irrigation conduit laid out over a vast expanse of cultivated land. Water is pumped out of available sources of supply, such as irrigation canals, and delivered through the distribution network to the cultivated land. Although such a system may be capable of delivering large volumes of water, the system pressure may be too low for the most effective operation of the patented strainer. In order to adapt such a system for most effectively using the patented strainer, it is necessary to provide higher pressure such as by replacing existing pumps by higher pressure ones, or by adding separate boost pumps. Accordingly, the owners of such systems may be deprived of the benefits that can be obtained through the use of the patented strainer if they are not in a position to make rather major changes to their existing installations.
The present invention is directed to improvements in rotary self-cleaning strainers for the purpose of enabling a strainer of the type disclosed in U.S. Pat. No. 4,822,486 to be most effectively used in certain irrigation applications without the need to augment the existing water pressure in these systems. Briefly, the present invention comprises the modification of the patented strainer in such a way that comparable screen cleaning action can be accomplished at lower pressures.
When the patented strainer is operated at less than intended pressure, the reduced force directed from the nozzles against the screen has a compound effect: 1) the rotational speed of the screen is reduced; and 2) the force for dislodging debris from the screen is also reduced. Hence, a given area of the screen is cleaned less frequently, thereby, allowing more debris to be adhered at any given time, and only lower impact forces are available for dislodging the accumulated debris from the screen.
The present invention provides a solution for avoiding these detrimental effects of reduced pressure operation and involves the addition of a second set of nozzles, 180 degrees from the first set and acting on the screen in the same sense as the first set of nozzles. Now, adhering debris can be dislodged twice as often even though the screen continues to turn at reduced speed. The reduced impact force of the water against the adhering debris is effective in dislodging the debris since there is less time for debris to accumulate on a given area of the screen between cleanings by a set of nozzles and, therefore, there should be less debris to dislodge, on the average. Thus, a screen embodying principles of the improvement of the present invention can be used for existing irrigation, or other pump-out requirements, without the necessity of making major modifications to existing hardware.
A further aspect of the invention arises in the context of situations where fine particulate materials must be filtered, in addition to a variety of larger forms of assorted debris. It has been discovered that replacing one screen by another may not be sufficient to provide the proper construction for enabling the screen to be both suitably rotated and cleaned by one or more sets of nozzles. This aspect of the invention comprises constructing the screen in the form of a perforated cylindrical sheet girdled by a fine mesh woven screen.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.